PPARGC1A and neoplasm: In addition, PD-1 suppresses peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), a key metabolic regulator and transcriptional co-activator [97,129], which functions to maintain mitochondrial fitness in tumor-infiltrating lymphocytes [130], whereas blockade of the PD-1 signal enables PGC-1α activity to enhance glucose uptake and partially reverse the metabolic defects.